The progression from MDS to AML in older adults, or following chemotherapy, is an important clinical model for the study of carcinogenesis. The long latent period from exposure to development of disease, and the gradual evolution from pre-MDS, to MDS, to AML, argues strongly in favor of a multi-step process f carcinogenesis in which tumor suppressor gene (TSG's) are implicated. The complex karyotypes observed in these disorders usually involve chromosomal loss or deletions further reinforcing the concept of TSG's . Among the deletions in our clinical series, 5q, 7q, and 20q are consistently seen and are associated with specific clinical features suggesting the presence of TSG's. Our long term goal has been to identify these genes with a particular emphasis on 5q; continued deletion mapping and clinical correlations will further this goal. This is addressed in the first two Specific Aims: 1) To better delineate the chromosomal regions implicated for tumor suppressor genes on 5q, 7q, and 20q and to correlate them with clinical features. 2) When the del(5q) TSG is identified in a parallel project, to identify mutations in individual cases, characterize their structure-function relationships, and correlate with disease features. A secondary goal of our project involves the analysis of the MADR5 gene which we identified as a potential TSG. We believe that MADR5 and related genes play a critical role in signaling by TGF-beta, an inhibitory pathway that has only recently been recognized in the regulation of normal hematopoiesis, and is often disrupted in MDS-AML. The TGF-beta signaling pathway has not been studied in myeloid cells. Thus our last two aims are: 3) To elucidate the mechanics of TGF-beta signaling via MAD%5 and related genes in normal hematopoiesis; and 4) To determine the role of TGF-beta signaling in leukemogenesis, emphasizing cases with demonstrated TGF-beta resistance. These studies will help us to identify new TSG's in MDS-AML and understand their clinical significance, and may provide insight into their therapeutic manipulation.